JPH01184293A - Production of iodine and iodate - Google Patents

Abstract

PURPOSE:To perform efficient electrolysis at high current density and to produce iodine with high productivity by dividing an electrolytic cell into anode and cathode chambers with a cation exchange membrane as a diaphragm and electrolyzing an electrolytic soln. contg. an iodine compd. in the anode chamber to form iodine in the anode chamber. CONSTITUTION:An electrolytic cell 4 is divided into an anode chamber 2 and a cathode chamber 3 with a cation exchange membrane 1 as a diaphragm. The membrane 1 is preferably a fluorine-contg. cation exchange membrane having sulfonic acid or carboxylic acid groups as ion exchange groups and exhibiting superior oxidation and alkali resistances. An electrolytic soln. contg. an iodine compd. such as KI is electrolyzed in the anode chamber 2. I2 is formed in the chamber 2, K ions, etc., move to the cathode chamber 3 through the membrane 1 and a cathode reaction takes place to form KOH, etc. An iodate such as KIO3 can be obtd. from the formed I2 and the alkali such as KOH formed in the chamber 3 as required.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to the production of iodine and iodate salts, and particularly to a method for obtaining iodine and iodate salts by electrolysis.

(Prior art and its problems) Iodine (I2) is a chemical that is useful in pharmaceuticals and chemical industries, and as a starting material for obtaining various iodine compounds, and iodate is also used industrially as an oxidizing agent. It is a very important drug.

Conventionally known methods for obtaining iodine include a chemical reaction in which copper sulfate, sulfuric acid, ferrous sulfate, etc. are added to a solution containing an iodine compound to liberate iodine, and a method for obtaining iodine by electrolysis.

Iodates can also be obtained by electrolysis or the like.

The method of obtaining iodine by electrolytic reaction has a problem in that efficiency is low because iodine (I2, I3-) is produced at the anode and iodine is decomposed at the cathode.

(Object of the Invention) The present inventor has arrived at the present invention as a result of earnestly pursuing a method for producing iodine and iodate salts that does not have the drawbacks of these conventional techniques.

An object of the present invention is to provide a method for producing iodine and iodate salts, which can perform an electrolytic reaction efficiently, can perform electrolysis at a high current density, and has good productivity. The purpose is to

(Means for Solving the Problems) The present invention firstly performs diaphragm electrolysis on the iodine compound-containing electrolyte in the anode chamber of an electrolytic cell separated by a cation exchange membrane to generate iodine in the anode chamber side. This is a method for producing iodine characterized by the following: Second, diaphragm electrolysis is performed on the electrolytic solution containing an iodine compound in the anode chamber of the electrolytic cell separated by a cation exchange membrane to produce iodine on the anode chamber side. This is a method for producing an iodate, which is characterized in that an alkali iodate salt is obtained from the produced iodine and alkali.

(Function) Hereinafter, the case where potassium iodide is used as the iodine compound of the present invention will be explained in more detail.

In an electrolytic cell divided into an anode chamber and a cathode chamber by a cation exchange membrane, iodine (I2, r, -) is produced by electrolysis of a potassium iodide solution in the anode chamber (1 type, 2 type).

2K I →Iz +2K + 2 e
(1) I2+I-→ 1. ,−(
2) Potassium ions pass through the cation exchange membrane and move to the cathode chamber, and along with the cathode reaction, potassium hydroxide is produced as a by-product (Equation 3).

2 +2HzO+2 e→2KOH+H2↑ (3)
In conventional electrolysis methods that do not use a cation exchange membrane, the following decomposition reaction of iodine generated as a cathode reaction occurs (
4), the production efficiency of iodine was low, but in the present invention, the cation exchange membrane prevents iodine (I2.13) from entering the cathode chamber, so the production efficiency of iodine becomes high.

13-+2 e I3 I-(4) The generated iodine can be precipitated using the solubility difference,
Iodine (I2) can be obtained as a simple substance by adding sulfuric acid to precipitate iodine (I2) or by conventional methods such as distillation, but it may also be used as is as an iodine-containing solution.

To obtain an iodate, alkali hydroxide may be added to the iodine obtained in formulas 1 and 2 (formula 5), or it may be added separately. Alternatively, the anode chamber may be made strongly alkaline in advance and the reaction may be carried out within the anode chamber.

3I2 + 6KOH→ KIO:l +5KI +
31120 (5) This iodate can be extracted as crystals by crystallization or the like, or can be used as a solution.

(i) Electrolytic cell The electrolytic cell used is not particularly limited. Even if a box-shaped electrolytic cell is used, which is divided into one anode chamber and one cathode chamber using cation exchange membranes, which will be described later, it is also possible to divide the cell into multiple anode chambers and cathode chambers using multiple cation exchange membranes. Configures a bipolar electrolytic cell,
It may be a box-shaped electrolytic cell in which the electrolytic solution circulates through a plurality of electrolytic chambers.

(ii) Electrolytic conditions For the production of iodine, it is preferable to perform electrolysis under the following conditions.

Electrolyte temperature: 20 to 110°C Current density: 2 to 50 A/dm2 Anode chamber pH: 8 or higher Cathode chamber: pH 12 or higher The higher the temperature, the lower the voltage between electrodes and the amount of power used, so 20°C is better. More preferably, 40°
C or higher is good. If the current density is too low, productivity will decrease,
If it is too high, the inter-electrode voltage will rise and the amount of power used will increase, so the above range is better, but more preferably 5 to 30 A/d.
It is 2.

It is preferable to perform electrolysis at a pH of 8 or higher on the anode chamber side.

This is because the iodine generated at the anode requires time to dissolve in the iodine compound electrolyte, and the dissolution rate varies depending on the hydrogen ion concentration of the iodine compound electrolyte. Therefore, electrolysis is performed at a high current density as in the present invention. This is because, if the pH is below 8, the generated iodine will not be fully dissolved in the iodine compound electrolyte. Further, since the rate of production of iodine exceeds the rate of dissolution of iodine into the iodine compound electrolyte, a phenomenon occurs in which the voltage increases. Therefore, in order to perform electrolysis at a pH of 8 or lower, it is necessary to take measures such as lowering the current density.

As mentioned above, alkali hydroxide is formed as a by-product in the cathode chamber, making it strongly alkaline, making it difficult to operate at a pH of 12 or less, but there is no particular problem as long as the electrical conductivity of the electrolyte is kept high. Further, in order to utilize this alkali hydroxide as a by-product, it is advantageous to have a higher concentration.

(iii) Cation exchange membrane There are hydrocarbon-based and fluorine-based cation exchange membranes, but they produce oxidizing iodine in the anode chamber and alkali hydroxide in the cathode chamber. It is preferable to use a cation exchange membrane having excellent oxidation resistance and alkali resistance, particularly a fluorine-based cation exchange membrane having a sulfonic acid group and/or a carboxylic acid group as an ion exchange group.

(iv) Since an oxidation reaction occurs, an insoluble anode is preferable in order to prevent electrode consumption, and an electrode coated with a platinum group metal such as platinum, iridium, and ruthenium or an oxide of a platinum group metal as an electrode active material. or lead oxide electrodes.

In addition, as mentioned above, the production of iodine and the dissolution of iodine into the iodine compound electrolyte compete with each other, so it is necessary to make the dissolution of iodine faster, so it is necessary to improve the flow of the electrolyte on the electrode surface. Particularly good examples include electrodes processed into a wave or step shape, porous electrodes with small holes, and mesh electrodes.

(V) Iodine compound electrolyte The composition of the anolyte is particularly good if the main component is potassium iodide and/or sodium iodide as the iodine compound. It can also be used by adding other iodine compounds, acids and alkalis for pH adjustment, conductive salts, etc.
It is desirable that the concentration of the iodine compound, which is the main component, is 0.5 to 5 M/2. However, in the method for producing iodate, when an alkali metal compound (for example, potassium iodate or sodium iodate) is intended as the salt, it is necessary to use a composition in which a small amount of alkali metal is mixed.

In addition to the anolyte composition described above, the composition of the catholyte may be an alkali, a conductive salt, or the like, and since alkali is generated as electrolysis progresses, the catholyte may be composed only of water.

Examples of the present invention will be described below.

Iodine and iodate were produced using the apparatus shown in FIG.

(Example 1) A box-shaped electrolytic cell 4 with a length of 20 cm, a width of 40 c+n, and a depth of 30 cm is divided into an anode chamber 2 and a cathode chamber 3 using a fluorine-based cation exchange membrane 1 (trade name: Nafion). A platinum-plated titanium mesh with a length of 18 cm, a width of 25 cm, and a thickness of 0.2 cm processed into a mesh shape was used as an anode 6 and a cathode 7, and suspended in the electrolytic cell 4 so that the distance between the electrodes was 1 cm. did.

The anode chamber 2 is filled with an aqueous solution 102 containing 456.6 g of potassium iodide per 1°C and adjusted to pH = 12.8, and the cathode chamber 3 is filled with an aqueous solution 102 containing 16.8 g of potassium hydroxide per 12. , anode chamber 2 and cathode chamber 3
The inside of the tank 4 was stirred by the stirrer 5 inside.

When electrolysis is carried out while maintaining the liquid temperature at 50°C and the current density at about 20A/dm, the pH of the anode chamber 2 decreases within 6 hours.
decreased from 12.8 to 8.1, and iodine (I2, I3-
) is generated, and at the same time, potassium hydroxide is produced as a by-product in the cathode chamber 3, and during this time the interelectrode voltage increases from 4.8■ to 5.4■
It changed to

In addition, the total amount of iodine (I2, I3-) generated was 19.6
equivalent amount, and the current efficiency was 97.3%.

Furthermore, 16.8 equivalents of potassium hydroxide were generated at the cathode 7, and the current efficiency was 83.4%.

When electrolysis was carried out for another hour, the pH of the anode chamber 2 was 9.
．． During this period, the interelectrode voltage decreased from 5.4 to 15. OV, a current of only 2.5 A/dm2 was flowing, and a phenomenon occurred in which iodine could not be completely dissolved in the electrolyte. Therefore, when potassium hydroxide solution was added to the anode chamber 2 until the pH reached 8.2, the voltage between the electrodes was 9.6.
■The current was reduced to 20A/dm2.

After 7.5 hours of electrolysis, the two solutions in the anode chamber were taken out and divided into two. Dilute sulfuric acid was added to one to adjust the pH to 1.6 and iodine (I2) was extracted, and the other was heated to 0°C. A mixture of iodine and potassium iodide was obtained. In particular, the former had higher iodine purity than the latter. In both cases, it was possible to obtain highly pure iodine by distillation.

(Comparative Example) Iodine was produced in the same manner as in Example 1 except that the cation exchange membrane 1 of the apparatus shown in FIG. 1 was removed. 1 for electrolytic tank 4!
Contains 456.6 g of potassium iodide, pH=1
Aqueous solution adjusted to 2.8 20! The inside of the tank was stirred using the stirrer 5.

Electrolysis was carried out while maintaining the solution temperature at 50° C. and the current density at about 20 A/dm 2 . After 6 hours of electrolysis, the solution turned pale yellow.

The total amount of iodine (z, l3-) generated was 1.3 equivalents, and the current efficiency was 6.5%. The iodine once generated by the reaction at cathode 7 was decomposed, and the amount was significantly lower than in Example 1.

(Example 2) A box-shaped electrolytic cell 4 with a length of 20 cm, a width of 40 cm, and a depth of 30 cm was divided into an anode chamber 2 and a cathode chamber 3 using a fluorine-based exchange membrane 1 (trade name: Nafion), and a diamond-shaped mesh was formed. The anode 6 and the cathode 7 were made of platinum-plated titanium mesh with a length of 18 cm, a width of 25 cm, and a thickness of 0.2 mm, and were suspended in the electrolytic cell 4 so that the distance between the electrodes was 0.2 cm. supported.

1 in anode chamber 2! Aqueous solution 1 containing 456.6 g of potassium iodide and adjusted to p' H = 13', 2
0ffi and potassium hydroxide 16 per 1 in cathode chamber 3
．． The inside of the tank 4 is stirred by the stirrer 5 in the anode chamber 2 and the cathode chamber 3, the liquid temperature is maintained at 50° C., the current density is maintained at about 20 A/dm2, and the anode chamber 2 is When electrolysis was carried out while adding potassium hydroxide so that the pH did not fall below 13, 33.2 equivalents of potassium iodate were produced in 10 hours, and the current efficiency was as high as 98.9%. Ta. Further, the voltage during electrolysis was 2.1■, which showed almost no change.

After 6.0 hours of electrolysis, the anode chamber 2 liquid and tank 4
The precipitated crystals were taken out, cooled to 15°C, and the precipitated crystals were taken out, yielding highly pure potassium iodate crystals.

(Effects of the invention) The present invention provides the following effects when producing iodine and iodate salts:
The iodine compound-containing electrolyte in the anode chamber of the electrolytic cell separated by a cation exchange membrane is subjected to diaphragm electrolysis to generate iodine in the anode chamber side to obtain iodine, and the generated iodine and alkali generate iodine acid. Trying to get some salt.

The present invention is a highly productive method for producing iodine and iodate, which enables efficient electrolytic reaction and high-density electrolysis.Also, since electrolysis can be performed at low voltage, not only current efficiency but also Good current efficiency.

Furthermore, the cathode has other effects, such as the ability to obtain industrially valuable by-products such as alkali and hydrogen, making it a great contribution to industry.

[Brief explanation of the drawing]

The figure is a flowchart showing one aspect of the present invention for detailed explanation of the present invention. DESCRIPTION OF SYMBOLS 1... Cation exchange membrane, 2... Anode chamber, 3... Cathode chamber, 4... Electrolytic cell, 5... Stirrer, 6... Anode, 7... Cathode. Applicant Tanaka Kikinzoku Kogyo Co., Ltd.

Claims (2)

[Claims] (1) A method for producing iodine, which comprises performing diaphragm electrolysis on an iodine compound-containing electrolyte in an anode chamber of an electrolytic cell separated by a cation exchange membrane to produce iodine in the anode chamber side. (2) Electrolyte containing an iodine compound in the anode chamber of the electrolytic cell separated by a cation exchange membrane is subjected to diaphragm electrolysis in the electrolytic cell to generate iodine on the anode chamber side, and the generated iodine and alkali form an alkali iodate. A method for producing iodate, characterized in that it obtains.